1. Field of the Invention
The present invention relates to a power source device for a camera having accumulators chargeable as secondary batteries with the current resulting from the electromotive force of solar batteries.
2. Description of the Prior Art
Generally, minute primary batteries with small capacity such as silver batteries, mercury batteries and so on, are typically used as the power source for the light measuring circuit, the control circuit and so on, of a camera. However, the electromotive force of these batteries lowers due to battery discharge. Consequently, when the electromotive force lowers, the shutter operation and so on, of the camera become partially or totally impossible. Recently, the electronic techniques in the camera field have made remarkable progress, and there is a consequent tendency to increase the power consumption in various circuits of the camera. Accordingly, the electromotive force of the power source is often abruptly lowered so as to bring the camera into a non-operative state. This kind of difficulty can be overcome by changing the consumed battery for a new one, so that it is necessary for the photographer to carry the spare battery all the time during his photographing, which is inconvenient.
For this reason, it has been proposed that solar batteries and accumulators as secondary batteries, such as Ni-cd batteries and so on, be built in a camera so that the secondary batteries are always charged by means of the current due to the electromotive force of the solar batteries, so that this arrangement be used as the power source for the electrical circuit of the camera. In this way, the secondary batteries are always charged by means of the solar batteries so that a considerably long life can be obtained as compared with the power source system having primary batteries. However, the electromotive force of the solar battery unit is as low as 0.6 V even in the no-load condition. Accordingly, it is necessary to connect a plural number of the solar battery cells in series in order to obtain a sufficient voltage for charging the secondary battery as a power source for a camera with, for example, 1.3 to 6 V.
Thus, in the case of the conventional camera in which solar batteries are built, as is shown in FIG. 1, a plural number of the solar batteries 1.sub.1, 1.sub.2, 1.sub.3 -1.sub.n connected in series charge the secondary battery 4 through the non-return diode 2 and the charge current limiting resistance 3. To this secondary battery 4, the control circuit 6 of the camera is connected through the power switch 5. By connecting a plural number of the solar batteries 1.sub.1, 1.sub.2, 1.sub.3 -1.sub.n in series in this way, a sufficient photo-electromotive force can be obtained, so as to charge the secondary battery. However, when a plural number of the solar batteries 1.sub.1, 1.sub.2, 1.sub.3 -1.sub.n are connected in series, even if the light incident upon only one of the batteries is shaded, no current from the electromotive force of the batteries can be obtained due to the property of solar batteries.
In order to solve this problem, it has been proposed that a plural number of solar batteries be connected as is shown in FIG. 2. For example, 16 solar batteries 1.sub.a, 1.sub.b, 1.sub.c -1.sub.p are divided into four groups, each consisting of four serial-connected batteries, while the groups are connected in parallel in such a manner that the composed output of the groups charge the secondary battery 4 through the non-return diode 2 and the charge current limiting resistance 3. To this secondary battery 4, the control circuit 6 of the camera is connected through the power source switch 5. In this way, a certain number of solar batteries are divided into several battery groups, each consisting of several serial-connected batteries, while the battery groups are connected in parallel in such a manner that even if the light incident upon one or two solar batteries were shaded, a sufficient photo-current for charging the secondary batteries can be obtained. In the case of the system in accordance with which a plural number of solar batteries are connected, a sufficient photo-current can be obtained under high brightness, while it cannot be obtained under low brightness.
Further, the plural number of solar batteries shown in FIGS. 1 and 2 are provided on the front plane of the camera body so that there is a possibility that the light incident upon several solar batteries may be shaded depending upon the holding condition of the camera at the time of photographing.
In FIG. 3, 10 is the camera body, 11 is the pentagonal prism cover and 12 is the photographing lens and 13a and 13b are the battery units, each being composed of eight solar batteries provided on both sides on the front plane of the camera body 10. 14a and 14b show the hands of the photographer during photographing. As is shown in the drawing, a part of the solar battery units 13a and 13b is shaded by means of the hands of the photographer. That is, the light incident upon some solar batteries is partially or totally shaded. Consequently, in a system in accordance to which a plural number of solar batteries are connected as is shown in FIG. 1, no photo-current can be obtained, while in a system as shown in FIG. 2, sufficient photo-current cannot be obtained.